RDB rotor opening milling?

Discussion in '40- & 55-Series Tech' started by e rock, Nov 9, 2005.

  1. e rock

    e rock

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    Ok - this ought to be a quick easy one...

    When getting GM rotors milled to fit over the axle flange, what's the appropriate ID?

    I've seen 4.185", 4.21", 4.25".

    I don't have a spare rear to measure and my caliper doesn't fit inside my wheel. Judging by the gap between the hole in my wagon wheels and both the rear flange and the front lockout hub, they're very similar. When I measure the OD of the lockout hub (I have the old coffee-can style warns) I get about 4.12".

    Perhaps the most important question: Is there any reason NOT to just get them milled to 4.25" ?

    Also, the guy that's doing mine is a wheeler and usually adds a chamfer to the inside edge where it would meet the flange. Is this necessary or prudent?


    Thanks,
    Eric
     
  2. Degnol

    Degnol

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    I had mine done to 4.185, Had to really clean the flange on the axle, paint, dirt grease, etc, and tapped them on witha rubber mallet. Actually the lugnuts would have sucked them up but I wanted to make sure they fit.
    I think the closer the better. The tighter they fit the flange, the less strain on the studs. Chamfer? sounds OK to me
    GL
    Ed
     
  3. cardinal fang

    cardinal fang

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    4.20" Measured on a 73 and 75 axle.
    The lug nuts on the lugs will center the rotor on the axle end. If you are using the stock nuts, or that style.

    Go to my webpage and read the writeup there.
     
  4. Degnol

    Degnol

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    I just followed this and everything worked out fine.

    http://www.birfield.com/~morgan/tech/rdb/index.html


    I still maintain that you want the smallest hole that will fit flush. For me that was 4.185. Of course anything larger will fit.


    Ed

    Fang, did not see your writeup until mine was done. Thanks for writing it, but can't you post it in Tech Links, or rather link it to Tech Links?



    Ed
     
  5. hodag

    hodag

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    I did mine to 4.2 with a chamfer. No problems yet after 3.5 years.

    Hodag
     
  6. Pin_Head

    Pin_Head

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    If you have trouble finding a shop to do this, you can use the po white trash rotor lathe method:

    Jack up rear end put on jack stands, block front tires and remove tire, drum.
    Install lug nuts backward on flange.
    Install rotor, and use more lug nuts to retain rotor.
    Start engine and engage 4th gear.
    Remove metal from inside of hole of spinning rotor using a mill file.

    WARNING: this method may qualify you for a Darwin award.
     
  7. miker

    miker

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    My rotors are machined a bit large for my axle flanges. I'm using stock lug nuts and aftermarket steel wheels and the conical part of the nut does not protrude through the wheel far enough to engage and center the rotor. If I think about it, it doesn't make sense that it should since if it did, it would not secure a wheel before bottoming out on a stock brake drum configured Land Cruiser.

    I'd suggest machining for a snug fit.

    Otherwise, the only way to center the rotor for me is to install a few nuts conical side towards rotor (without the wheel installed) and tighten them. Then have someone hold down on the brakes while I remove the lugs, install the wheel, and then reinstall and retighten the lugs.
     
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